Agronomic components of rice crops at different yield levels
1998
Torres, R.O. | Sheety, J. | Kropff, M. | Cassman, K. (International Rice Research Inst., P.O. Box 933, 1099 Manila (Philippines))
The principal agronomic components of a rice crop that would contribute to yield increase were studied using IR72 in two dry season experiments at IRRI, Los Banos [Laguna, Philippines]. Three levels of nitrogen fertilizer were used: O N, 225 kg N/ha and a sustained weekly application of 40 kg N/ha starting from transplanting to 2 wk after flowering or a total of 440 kg N/ha. Results of these studies are useful both in developing breeding and management approaches for a high-yielding rice crop. The number of tillers doubled by increasing the N fertilizer rate. However, the number of unproductive tillers increased correspondingly up to about 50 percent of the total. The rice reproductive stage was about a week longer with sustained N fertilizer compared with the unfertilized crop. The number of grains per square meter increased by more than 100 percent with sustained N application and produced a grain yield of 12.6 t/ha despite a 12.7 percent decrease in filled grain percentage and a 10.5 percent decrease in unit seed weight. The rice crop took up 83 kg N/ha without N fertilizer, but more than 200 kg N/ha was taken up to produce 10 t grains/ha. These results showed a high demand for N fertilizer to produce high grain yields. This amount could not be obtained from the inherent soil N. The production of unproductive tillers was probably a wasteful use of N and energy. A cultivar with fewer unproductive tillers and with greater resistance to lodging even at high N fertilizer rate is desirable
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